ext4 — файловая система нового поколения

Теодор Тсо — один из авторов наиболее популярной файловой системы Linux ext2/ext3 анонсировал создание ext4. В основе новой ФС лежат стабильность, обратная совместимость с ext2/ext3 и разумная сложность кода. Процесс разработки включает 4 этапа:

1. Создание новой кодовой базы в ядре 2.6 (первоначальное название ext3dev), помеченной как «экспериментальная»
2. Критичесике исправления из ветки ext4 будут попадать в ext2/ext3. Основная разработка будет вестись только в ext4.
3. Обязательная обратная совместимость с ext2/ext3.
4. Ориентировочно через 6-9 месяцев, когда будет завершен первый этап разработки и все новые улучшения будут добавлены, файловая система будет переименована в ext4.

copy-paste from http://www.linux.org.ru/profile/ram32/view-message.jsp?msgid=1471652
The concerns that were expressed can be summarized in the
following points:

* Stability. There is a concern that while we are adding new
features, bugs might cause developers to lose work.
This is particularly a concern given that 2.6 is a
«stable» kernel series, but traditionally ext2/3
developers have been very careful even during
development series since kernel developers tend to get
cranky when all of their filesystems get trashed.

* Compatibility confusion. While the ext2/3 superblock does
have a very flexible and powerful system for
indicating forwards and backwards compatibility, the
possibility of user confusion has caused concern by
some, to the point where there has been one proposal
to deliberately break forwards compatibility in order
to remove possible confusion about backwards
compatibility. This seems to be going too far,
although we do need to warn against kernel and
distribution-level code from blindly upgrading users’
filesystems and removing the ability for those
filesystems to be mounted on older systems without an
explicit user approval step, preferably with tools
that allow for easy upgrading and downgrading.

* Code complexity. There is a concern that unless the code is
properly factored, that it may become difficult to
read due to a lot of conditionals to support older
filesystem formats.